arm-fm-22k/lib_src/eas_pan.c

/*----------------------------------------------------------------------------
 *
 * File:
 * eas_pan.c
 *
 * Contents and purpose:
 * Calculates left and right gain multipliers based on a pan value from -63 to +63
 *
 * NOTES:
 * The _CMX_PARSER and _MFI_PARSER preprocessor symbols determine
 * whether the parser works for those particular file formats.
 *
 * Copyright Sonic Network Inc. 2005

 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 *----------------------------------------------------------------------------
 * Revision Control:
 *   $Revision: 82 $
 *   $Date: 2006-07-10 11:45:19 -0700 (Mon, 10 Jul 2006) $
 *----------------------------------------------------------------------------
*/

#include "eas_pan.h"
#include "eas_math.h"

/*----------------------------------------------------------------------------
 * EAS_CalcPanControl()
 *----------------------------------------------------------------------------
 * Purpose:
 * Assign the left and right gain values corresponding to the given pan value.
 *
 * This routine uses sin/cos approximations for an equal power curve:
 *
 * sin(x) = (2-4*c)*x^2 + c + x
 * cos(x) = (2-4*c)*x^2 + c - x
 *
 * where  c = 1/sqrt(2)
 * using the a0 + x*(a1 + x*a2) approach
 *
 * Inputs:
 * pan          - pan value (-63 to + 63)
 *
 * Outputs:
 * pGainLeft    linear gain multiplier for left channel (15-bit fraction)
 * pGainRight   linear gain multiplier for left channel (15-bit fraction)
 *
 * Side Effects:
 *----------------------------------------------------------------------------
*/
void EAS_CalcPanControl (EAS_INT pan, EAS_I16 *pGainLeft, EAS_I16 *pGainRight)
{
    EAS_INT temp;
    EAS_INT netAngle;

    /* impose hard limit */
    if (pan < -63)
        netAngle = -63;
    else if (pan > 63)
        netAngle = 63;
    else
        netAngle = pan;

    /*lint -e{701} <avoid multiply for performance reasons>*/
    netAngle = netAngle << 8;

    /* calculate sin */
    temp = EG1_ONE + FMUL_15x15(COEFF_PAN_G2, netAngle);
    temp = COEFF_PAN_G0 + FMUL_15x15(temp, netAngle);

    if (temp > SYNTH_FULL_SCALE_EG1_GAIN)
        temp = SYNTH_FULL_SCALE_EG1_GAIN;
    else if (temp < 0)
        temp = 0;

    *pGainRight = (EAS_I16) temp;

    /* calculate cos */
    temp = -EG1_ONE + FMUL_15x15(COEFF_PAN_G2, netAngle);
    temp = COEFF_PAN_G0 + FMUL_15x15(temp, netAngle);
    if (temp > SYNTH_FULL_SCALE_EG1_GAIN)
        temp = SYNTH_FULL_SCALE_EG1_GAIN;
    else if (temp < 0)
        temp = 0;

    *pGainLeft = (EAS_I16) temp;
}